1. Field of the Invention
The present invention generally relates to the filtering of liquids and more specifically to the filtration of high temperature, high pressure etching liquids primarily used in the processing of semiconductor devices and requiring an extremely low particle count and very high reliability.
2. Description of the Prior Art
Presently available filter housing assemblies use cartridges inserted into a cylindrical housing with a twist-screwtop to tighten an O-Ring against the housing flange for generating a sealed unit with an inlet and an outlet for the liquid to be filtered. Some assemblies are molded in one piece as a throw-away unit. The liquid enters under pressure through the inlet into the space between the housing and the cylindrical filter cartridge and is forced through the filter. The filter surrounds a concentric cylindrical space through which the filtered liquid exits from the outlet at the bottom of the filter housing. The filter cartridge is closed off at its top and has a nose at its bottom, surrounded by O-rings, by which the cartridge is held in the bottom recess of the filter housing. Potential shortcomings of the filter housing are damage to the O-ring because of twisting, deforming and abrasive action during screw-on closure, which can contribute to leakage and a decrease in filtration efficiency.
Usually the cartridge is inserted and held only at the housing bottom by two parallel O-rings around the cartridge nose. The filter cartridge may tilt as a consequence of fluid pressure action and no longer be concentric with the filter housing, causing an uneven flow through the cartridge. This action also may contribute to lower filtration efficiency and a higher particle count by uneven filtration or by bypassing of the filter as well as to lower filter cartidge life. Together with the used cartridge filter housings are customarily thrown away, amounting to economical and environmental waste.
Large cross-section vent tubes have been used to maintain an air-cushion in the housing cap for pressure variation dampening, which leads to a sizable amount of liquid being forced out the vent tube back to a pump, decreasing the filtration efficiency.